Collaborative activities such as coordination, decision-making and negotiation critically depend on historical knowledge of an organisation. Previous research in collaborative activities has proposed the use of collective memory to accumulate, organise, preserve, link and share diverse knowledge coming from past experiences, and thus support such collaborative activities. In this paper we describe a hybrid reasoning-based system for collaborative decisionmaking which combines a case-based reasoning method and a model-based reasoning method. The main goals are to reduce the time required to come to a decision, particularly, in a contingency situation, to compensate for lack of experience of young operators, and to distribute available experience to different sites.